1. Field of the Invention
The present invention relates to an image formation device in which beam light is employed to store an image data in an optical image memory, and the image stored therein is read and printed out.
2. Description of the Related Art
U.S. Pat. No. 3,796,999 discloses a display in which laser light selectively irradiates a liquid crystal cell to display an image on liquid crystal array. According to the invention disclosed therein, head of the laser light is utilized to partially change a phase of the liquid crystal, and an image can be formed depending upon an irradiation pattern of the laser light. The liquid crystal cell employed is, for example, a smectic liquid crystal.
Japanese Unexamined Patent Publication SHO/64-20773 discloses a device in which a thermal writing liquid crystal cell device is employed to form an image. According to the invention disclosed therein, transmitting light through a liquid crystal cell layer or reflecting light therefrom irradiates photosensitive material to make a latent image on the photosensitive material, and an image can be formed based upon the latent image. There are provided three kinds of liquid crystal cells where respective images of primary colors, red (R), green (G) and blue (B), are to be written, and a full color image is composed of the three types of images.
In such a conventional image formation device, formation of a variable density image on a liquid crystal cell can be implemented by varying energy of laser beam used for writing in accordance with density information of image data. A method of varying an irradiation energy of laser beam includes a amplitude modulating method in which an intensity of emission of laser beam is varied and a pulse width modulating method in which a period for which light is emitted is varied while the intensity of emission of laser beam is fixed, and because of simplicity and accuracy of control, usually the pulse width modulating method is employed. In this method, a gradation control of each pixel is implemented by varying on-time of laser within a range of a period of a pixel cycle in accordance with the density information of image data.
However, the on-time of the laser within the range of a period of a pixel cycle is continuous, and hence, there arises an unevenness in a distribution of applied energy within a single pixel, and a good reproduction of gradation cannot be obtained.
Accordingly, it is an object of the present invention to provide an image formation device in which a gradation reproducibility is enhanced by leveling the dispersion of the laser energy directed to a single pixel.